The present invention relates to a wrench, and more particularly to a power wrench.
A power wrench which is driven by bearing member is disclosed in U.S. Pat. No. 4,603,606 to Headen. A yoke 72 is actuated to rotate with a reciprocating arcuate motion by a rotation of a drive shaft 86 via a pivot ball 80, as shown in FIG. 6 of this patent. The cartridge 10 is driven by the arcuate motion of the yoke 72, and the shaft 16 is driven to rotate by the roller bearing 18. The shaft 16 should be stably held in position by a retaining force in order to prevent the shaft 16 from "backlash" when the core 20 of the cartridge 10 rotates backward. The retaining force should be overcome by the power driving the drive shaft 86. The efficiency thereof is increased on the order of 30% which is unsatisfactory.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional power wrench.